Method of and apparatus for recovering fluids from underground strata



June 6, 1933. E. P. HALLIBURTON METHOD OF AND APPARATUS FOR RECOVERING FLUIDS FROM UNDERGROUND STRATA D Filed Nov. 10, 1931 2 Sheets-Sheet, 1

Jimmy:

June 6, 1933. E. P; HALLIBURTON 1,912,573

METHOD OF AND APPARATUS FOR RECOVERING FLUIDS FROM UNDERGROUND STRATA Filed Nov. 10, 1951 '2 sheds-Shea, 2

' w I lnwntgr Patented June 6, 1933 UNITED- STATES EBLE PALMER EALLIBURTON, 011 LOS ANGELES, CALIFORNIA METHOD OF AND APPARATUS FOR RECOVERING FLUIDS STRA'I'A FROM UNDERGROUND Application filed November 10, 1931. Serial a. 574,118.

This invention relates to improvements in the art of withdrawing and recovering fluids such as mineral oil, from underground strata. More particularly, it relates to a method of 6 cementing combination strings of casings within a well hole whereby a perforated or slotted screen pipe or caslng may be positioned and properly cemented at or near the bottom of a well hole.

The invention also relates to means whereby proper circulation of mud fluid or other liquid may be obtained through the slotted or perforated pipe or casing.

Numerous methods of cementing casing in 1 well holes have been evolved heretofore.

Considerable dilficulty, however, has been experienced in cementing a combination string of casing. By a combination string, reference is made to a casing containing or including one or more lengths of slotted, perforated or other type of screen casing, such slotted or perforated screen being generally attached to the lower end of a string of imperforate casing of substantially the same diameter. When such combined string is placed within a larger casing, the lower end of the combined string extending'below the larger casing, and the string then cemented to ,the well hole below the large casing, such combined string may function as a combination string, oil passing through the central casing and water through the annular space between said central casing and the outer and larger casing. Heretofore, it has been difficult, if not impossible,-to place a screen pipe or casing in the bottom of a well hole and circulate water or a light mud fluid through such screen and combination string for the purpose of removing debris, detritus, cuttings and other material present in the bottom of a well hole.

This invention relates to a method by means of which it is possible to cement a casing in a well hole, the cementing action taking place slightly or immediately above the slotted or perforated casing. Another object of this invention is to disclose and provide means whereby circulation of mud fluid may be carried out through a string of easing having a strainer therein.

I or casing, without Another object of this invention is to dis close and provide, a strainer construction permltting circulation of a suitable fluid therethrough for a predetermined length of time.

Another object is to disclose and provide means whereby a well may be cemented at a point above slotted or er orated screen pipe lling, obstructing or clogging the slots or perforations with the cementing material.

These and other objects, uses and advantages of this invention will be apprehended by those skilled in the art from the following detailed description of illustrative examples of this invention.

In describing the invention, reference will be had to the appended drawings, in which Fig. 1 is a vertical section through the lower portion of a well hole.

Fig. 2 is an enlarged longitudinal section 70. through a part of the screen casing-shown in Fig. 1.

Fig. 3 is an enlarged longitudinal section through a part of screen casing prepared in accordance with this invention and adapted for use as in Fig. 1.

Fig. 4 is a vertical section through the lower portion of a well hole, illustrating one method and means em loyedin cementing the casing in said well liole.

Fig. 5 is a longitudinal section through a modified form of cementing valve adapted for use in this invention.

Fig. 6 illustrates the device shown in Fig. 5 in cementing position.

Fig. 1 illustrates a casing 2 cemented in the formation as indicated at 3. The casing 2 may have been cemented in any desired manner and the cement then drilled out to form the bore 4 and the well hole therebelow into a sand 5. The casing 2 may be one of several telescoping casings of progressively increasing size as these casings approach the surface of the ground. The central string which may be termed the oil string (in case 9 the sand 5 contains mineral oil), may consist of imperforate casin 6 jointed together by couplings or collars and a casing section 8 provided with a restriction orvwasher 9 restricting the cross sectional area of the casing at that point. Below the. casing section 8 may be one or more strings of screen casing 10 provided with suitable apertures, slits or perforations 11. The screen casing 10 may be connected to the casing section 8 in any suitable manner as, for example, by means of collars or couplings. A suitable guide shoe 12 may be carried by the lower end of the screen casin 10.

The use 0 perforated pipe or casing such as the section 10, is particularly advantageous in formations which are loose and shifting and which may readily cave in, thereby restricting or completely stopping the upward flow of oil from the sand 5. It is to be understood that during the drilling of the well hole 4 into the sand 5, a considerable amount of debris, detritus, cuttings, etc., may accumulate in the bottom of the well hole 4. During the withdrawal of the drilling tool and during and after the lowering of the oil string or combination string, sloughing may occur, partially filling the bottom of the well hole 4. For this reason, it is highly desirable to be able to maintain a circulation of mud fluid or other liquid through the entire length of the combination string 6 and through the annular space surrounding the string.

Heretofore it has been impossible to circulate through a combination string so as to cause the light mud fluid to be discharged from the bottom end of the string and be circulated upwardly through the well hole outside the screen to thoroughly wash and remove, cavings outside the screen. In normal practice, the fluid being pumped into the well is discharged through the perforations 11 of the screen or perforated casing, thus preventing the possibility of washing out the bottom of the well hole and removing the debris accumulated therein. In accordance with this invention, however, the perforations or openings 11 of the screen casing or pipe, are filled or closed with a substance capable of being removed either by the action of heat, pressure, the removal of a closure by drilling or disintegration, or by the continued action of water. A. positive circulation may thus be established through the end of the screen and throughout the outside of the screen and easing, without the use of complex packers or other devices.

In other words, the perforations 11 of the screen casing may be filled or closed with a substance which will effectively plug or close such openings until circulation has been carried out. Thereafter the substance employed in plugging the perforations in the screen casing may be removed.

Illustrative of this phase of my invention, reference is made to Fig. 2 wherein the sloted casing 10 provided with apertures 11 is shown provided with a filling material 13 in such openings or perforations 11. The substance used in sealing the openings 11 may be either removable by the continued action of water, b the action of heat, or in any other suitab e manner without withdrawing the screen casing from the well hole.

For example, the openings or perforations 11 may be filled with a sulfur compound in molten form. In preparing the string of perforated casing, the molten sulfur composition may be applied internally and/or externally of the slotted pipe or screen casing while such compound is in liquid form, and allowed to congeal or set within the various perforations 11, or the string may be mounted in a suitable chuck and spun on its longitudinal axis, the sulfur compound being introduced into the spinning casing in liquid form and distributed by centrifugal action into the various perforations 11.

During such spinning, the exterior of the perforated string may be wrapped with heavy paper or the like, to maintain the sulfur compound within the apertures 11. After spinning and after the sulfur compound hascompletely filled and set within the openings 11, the paper may be removed and the perforated casing lowered into the well hole.

After being lowered into the bottom of the well hole or into contact with the accumulated detritus at the bottom, the fluid being circulated through the string will be discharged from the lower end of the casing and not through the openings or perforations 11 inasmuch as such perforations or openings are sealed with the sulfur compound. After the string has reached the true bottom of the well hole or the position in which it is desired to maintain such screen pipe or casing, hot water may be admitted through the casing so as to soften, melt and remove the sulfur compound from the openings 11, thereby restoring the slotted or perforted casing to its original condition.

Instead of employing a sulfur compound or other similar composition capable of being melted and removed from the apertures 11 by the action of heat, the openings 11 may be filled with a plastic composition containmg ground bentonite, barytes, etc. and the inner surface of the screen pipe or casing coated with a layer of cemetitious material capableof setting and maintaining its strength for a desired time and also capable of disintegrating under the continued action of water. A cementitious composition answering these requirements may be made by mixing Portland cement with a solution containing a crystallizable salt in sufficient quantity to prevent a major portion of the cement particles from hydrating in bonding contact with each other. For example, if Portland cement is mixed with a relatively small amount of watercontaining a high proportion of calcium chloride, the resulting mixture will set but calcium chloride crystals will form throughout the mass, these crystals a cementitious composition of the character described hereinabove, such as for example passing through the casing lined with said composition, and the cementitious coating will eventually disintegrate and-be washed away. I

It will thus be seen that a casing lined with the casing 10 lined with the cementitious composition 14 shown in Fig. 2, may be attached to the lower end of an oil string and circulation of fluid may be established through such prepared perforate casing for an appreciable length of time before the cementitious coating 14 will disintegrate and permit the fluid to pass through the apertures 11. By properly proportioning cement, calcium chloride and water, the resulting cementitious mixture may be caused to withstand the pressure of the circulating fluid for any desired time interval, say 12 hours, 24 hours, 48 hours, etc.

Instead of employing calcium chloride, any other crystallizable salt solution may be em-. ployed. For example, I have found that suitable cementitious compositions capable of being used as a lining or filling for perforate casing may be made'by employing compositions consisting of Portland cement, and molasses or sugar solutions. During the setting of the cementitious composition, sugar crystals are formed between the particles of Portland cement so that the dried cementitious mass exhibits considerable strength. When such cementitious composition is exposed to the action of water, however, the Water soluble crystals of sugar go into solution in the water, thereby causing a partial disintegration of the cementitious body.

Water soluble salts of high water of crystal lization content such as aluminum sulfate, iron sulfate, the various alums, calcium phosphate, sodium phosphate, citrate, sulfate and tetraborate and others, are adapted for use in cementitious compositions of the character described hereinabove.

It is not necessary that the cementitious body or lining placed upon the inner surfaces of the perforate pipe or casing be completely removed by the action of the fluid circulated through the casing; it is merely suflicient that the continued circulation will in time so weaken or partially disintegrate the body that it may be readily removed subsequently by a suitable tool lowered into the casing.

Illustrative of the compositions which may be employed in sealing the openings in the perforate pipe or casing, it may be said that a compound consisting of 100 parts of cement, 6 parts of calcium chloride, 50 parts of sugar and 40 parts of water, results in a cementitious body capable of setting and dryin without the formation of cracks and in e ectively sealing the apertures in a slotted, perforated or other screen pipe or casing. This composition will be substantially disintegrated when water is passed through the casing under pressure for a period of about one hour. By decreasing the amount of sugar or by increasing the amount of cement, the time interval during which water may be passed through the casing without being discharged through the apertures of said casing, may be materially increased.

Another method of temporarily sealing the openings in perforated or screen pipe or,

comprises the application of a thin layer of sodium silicate to the interior surfaces and perforations of the screen casing. The coated interior surface of the screen casing may then be provided with a thin coat of cementitious material such as, for example, a neat Portland cement grout; The sodium silicate coating is preferably allowed to set before the Portland cement liner is formed within the casing. When a casing prepared as described hereinabove is then used in a combination string, it will be found that the fluid passing through the casing will eventually soften and dissolve the sodium silicate, permitting the entire central lining of Port-- land cement to separate from the wall and slough off to the bottom of the hole. Or such inner liner of cement, may be subsequently removed by a drilling tool lowered through the casing.

Those skilled in the art will apprehend that wherever reference is made herein to a cementitious composition, such reference embraces not only compositions containing hydraulic cement, but other compositions as well, capable of setting or drying to form a body adapted to withstand the action of fluid ed condition, asbestos, etc., as the presence of such fillers and reinforcing agents tends to raisethe melting point of the resulting composition. In addition, fusible metallic compounds and alloys may be employed such as, I

for example, Darcets metal, Newtons metal, etc., instead of the cementitious compositions mentioned hereinabove. An alloy comprising 25% of tin, 25% of lead and 50% of bismuth, has a melting point of about 93 C. An alloy containing 35% of tin, 45% of lead and 20% of bismuth, has a melting point of about 150 C. Numerous metallic compositions having relatively low melting points are known and such metallic compounds may be applied to the perforations of the screen pipe orcasing before such cas ng '1s lowered into the well-hole so as to permit circulation of fluid through the end of the screen, and after such circulation has removed the debris and permitted the casing to be properly positioned in the well hole,

such fusible metal may be readily removed from the perforations by a. suitable application of heat to the screen as,.for example, by steam injection.

The followin method of preparing screen pipe or casing, illustrated in Fig. 3, has. been found to be particularly effective and economical: A tough, parchment-like oiled paper 20. (such as stencil paper about 0.006 inches thick) is inserted into the screen pipe 10 to form an inner liner. Two thicknesses of stencil-type paper are desirable. A volume of cement slurry is then introduced into the lined screen, plugs inserted in the ends and the screen is spun for a desired length of time until a layer of cement 21 is formed onthe interior. During spinning, some water may be thrown off through the paper and openings in the screen. The finished screen, therefore, comprises an inner layer of cement separated from the screen pipe by a layer of iibrous material. This or any other prepared screen casing is then attached to the imperforate casing and valved casing section and lowered into the well.

It may be desirable not to seal all of the perforations or openings of the screen pipe or casing by a composition ofthe character described hereinabove. As shown in Fig. 1,

- all of the apertures 11 in the screen casing 10 may be so sealed but perforations 15 near the bottom end of such casing may be left open so as to permit a certain amount of fluid being passed down through the combination string to be discharged through such openings 15, thereby facilitating somewhat the removal of debris and the establishment of proper circulation in the bottom of the well hole. The fluid passed through the prepared screen pipe or casing may be a relatively thin mud fluid.

As shown in Fig. 1, the casing section 8, substantially of the same internal diameter as the casing 6, is provided with a plurality of valve members 16 inserted through a plurality of apertures formed in the casing section 8. These apertures are provided with walls which flare outwardly and the valve members 16 are wedged in such apertures and extend inwardly toward the center of the casing section. The valve members 16 may be made of wood, cast iron, or other brittle, easily sheared substance. The valve members 16, furthermore, are positioned above the retaining ring or restriction 9 carried by the casing section 8.

The various elements described hereinabove may be utilized in the following manner:

The casin or cementing section 8 may be attached to t e upper end of screen casing 10 and imperforate casing 6 may be attached to the upper end of the cementing device 8. The

screen casing may be prepared as has been described hereinabove, the apertures in said screen being sealed off by means of a suitable composition or liner. The assembled casing is then lowered into the well hole. Circula tion of mud fluid is established downwardly through the casing and screen and upwardly through the annular space separating the screen and easing from the walls of the well hole. Such circulation is preferably maintained until all debris, cavings, etc., are re moved from the well hole so that a mud fluid of substantially uniform gravity exists within the casing and in the annular space surrounding the same. In order to cement the casing in the well hole at a point immediately above the screen, a plug known as a bottom plug 17 is inserted into the top of the casing on top of the mud fluid existing therein. A proper amount of cement slurry is then introduced on top of the plug 17 and such cement slurry pumped into the casing, forcing mud fluid from the casing through the bottom of the screen. The plug 17 is preferably made of wood or other easily destroyed material and should be of a size slightly smaller than the interior diameter of the casing. It may be provided at its upper end with a flexible gasket 18.

The plug 17 and the cement slurry thereabove is forced downwardly through the casing 6 and finally comes in contact with the inwardly extending ends of the valve members 16. Under the influence of pressure of the cement slurry, the plug 17 breaks off the inwardly extending ends of the valve member 16 and comes to rest upon the restriction 9 carried by the cementing casing section 8. The plug 17 then occupies a position between the restriction 9 and the ports 19 in which the valves 16 have been held.

A second plug known as the top plu is then introduced into the-casing on top of the cement slurry. This top plug may be provided with'a measuring line. A suitable hydraulic fluid is then introduced into the casing on top of the top plug and the top plug forced downwardly through the casing, forcing the cement slurry below said top plug out through the ports 19. The valve members 16, formerly retained in said ports, are blown out by the head of cement slurry and the ressure with which said cement is being orced into the casing. Inasmuch as the lower end of the well hole is filled with a qluiescent mud fluid, the cement slurry e ected t rough the ports 19 follows the line 0 least resistance and moves'upwardly through the annular space between the casing 6 and the well hole.

It has been found that the cement slurry will not settle downwardly below the ports 19 for any appreciable distance, the cement slurry being supported by the non-compressible and uiescent mud fluid remaining in the bottom 0 the well hole. By observing the measuring line attached'to the top plug, the application of pressure may be stopped when the top plug is within a certain pre etermined distance of the bottom plug 17 thus causing a predetermined thickness of cement to set within the casing 6. n i A Instead of employing a measuring line, a

spacer may have been introduced into the cement slurry immediately beneath the top plug. The cementitious slurry sets exteriorly of the casing 6 supported by and suspended above the screen pipe, eifectively cementing the casing to the well hole above the screen and thus preventin water or other material from points above t e screen 5 from passing down into the screen casing.

In the event that some settling or grading of the cement slurry may occur slightly below the ports 19, there is no possibility of having the cement plug up the apertures in the screen as such apertures have been closed with a sealing means.

After a. suitable time interval has elapsed and the cement slurry has set, drilling tools may be lowered through the'casin and cement remaining in the casin ,drllled out. The drilling also destroys an removes the plug 17 as well as the stop 9. The debris thus created may be washed and bailed out until all of the dbris as well as most of the mud fluid remaining ,in the screen casing 10 is removed.

By the time the drillingfools pass through the top plug, cement and ottom plug 17, e cementitious coating on the interior surfaces of the screen pipe 10 has disintegrated so that. it maybe readily and quickly removed by the drilling tool without incurring the possibility of unscrewing the screen casing.

from the upper portion of the combination string. Or the drilling tool may be lowered into the screen and the inner seal removed.

- The screen may be spot welded to the adbailing or circulation.

' Instead of employing the cementing casing at either end so as to threadedly engage with an imperforate casing 6 at one end and a screen casing 10 at the other end. The body portion of the device may be provided wit a plurality of peripherally spaced outwardly fiarlng ports 23. Valve means may be provided for normally keeping these ports closed. For example, poppet valve members 24 adapted to seat in the ports23 may be held in such ports by means of s ring members 25.

attached to'the body portion 22 in any suitable manner as, for example, by means of machine screws 26. v

-.A sleeve 27 may be slidably carried with- .in the tubular member 22. Such sleeve 27 may be provided with an inwardly extendlng stop of any suitable character. For example, a stop such as 9 in Figs. 1 and 4 may the body portion 22 of the device in position to cover the ports 23, may be provided. The sleeve 27 may be provided with a peripheral groove and the interior surface of the tubular member 22 provided with an inwardly extending bead as shown at 31. The. inner sleeve 27 may then be pressed into the tubular member 22 during assembly until the bead 27 on the interior surface of the tubular member 22 .enga es with the groove of the sleeve 27.

The orce required to release the friction hold thus made may be regulated, and noted during assembly. When in such engaged posierably in substantial abutting relation with the end of the casing 6 threadedly connected to the upper end of the tubular member 22. The bead and groove means here described not only function as a releasable means holding the sleeve in position over the ports 23 but in addition function as a seal preventing fluid from passing into the well hole.

Instead of the bead and groove friction hold, shear pins such as the pin 30 may connect the sleeve 27 with the tubular body portion 22 of the device. When thus connected, as shown in Fig. 5, the ports 23 are closed by the upperend of the sleeve 27.

Means may be provided for. preventing rotation of the sleeve 27 within the tubular body portion 22 of the device. Such means tion, the upper end of the sleeve 27 is prefmay comprise a pin 32 carried by the body portion 22 and extending inwardly and adapted to be slidably received in a longitudinal slot 33 in the lower end of the memher 27, said pin 32 being'adapted to enter and cooperate with the slot 33 when the sleeve 27 is moved downwardly so as to expose the ports 23.

After the string has been assembled, said string including the prepared perforated casing 10, the cementing device and the 1mperforatecasing 6, and such string lowered into the bottom ofithe well hole, circulation is maintained as described hereinabove until the entire well hole including the space surrounding the screen has been cleared of all dbris and all cavings, bridges, etc., removed. A bottom plug 17 is then inserted into the top of the casing on top of the mud fluid therein, this plug being of such size that it will pass down throughthe casing but will not pass through the stop or restriction carried by the sleeve 27 of the casing device. The bottom plug 17' may be provided with a suitable expanding gasket 18. A suitable charge of cement slurry is introduced into the casing on top of the plug and such cement slurry forced downwardly into the casing advancing the bottom plug 17 and displacing mud fluid in the. string. A top plug is inserted into the casing on topof the charge of cement, such top plug being followed by a suitable hydraulic fluid introduced to give suflicient pressure to force the cement slurry and bottom plug into contact with the restriction, stop or back pressure valve carried by the sleeve 27. A- suflicient pressure is built up within the casing 6 to cause the sleeve 27 to move downwardly and to release the friction hold between the sleeve 27 and the body portion 22 of the cementing device. Downward motion of the sleeve 27 uncovers the ports 23 and the cement slurry is then forced outwardly through the ports 23 into the annular space surrounding the cementing device and easing. As described hereinabove, the cement slurry rises upwardly in the annular space surrounding the casing 6. A suflicient quantity of cement slurry is allowed to remain within the casing 6 above the bottom plug 17' so that if any dilution or grading of the top portion of the cement slurry has occurred,-all such diluted or graded slurry will remain within the easmg.

If instead of the friction hold including the bead and groove construction described hereinabove, shear pins 30 have been used as the releasable means, the pressure of the cement slurry is suflicient to shear the pins 30 and move the sleeve 27 downwardly, thus uncovering the ports 23. The downward movement of the sleeve 27 causes'the pin 32 carried by the body portion 22 to engage 65 with the slot 33 of the sleeve 27.

After the cement hasset, any cement that may have been left in the casing is drilled out together with the two cementing plugs and the stop or back pressure valve carried by the sleeve 27. Rotation of the sleeve 27 within the body portion 22 is prevented dur ing this drilling operation by the pin 32. The lining or cement within the screen casing 10 may also be drilled out leaving the perforations of the screen open to the producing formation.

It will be understood that the slidable sleeve 27 instead of completely uncovering the ports 23 may be provided with similar ports which are in ofi'set relation when the sleeve 27 is in locked position within the tubular body portion 22 and in aligned position with the ports 23 when the friction hold or shear pins are released.

It will be apparent to those skilled in the art that a novel method of preparing screen pipe or casing has been disclosed whereby it is possible to circulate a fluid through a screen pipe .or casing while restricting the flow of fluid through the perforations of such screen. Positive circulation of mud fluid completely around the screen casing is insured. I

Furthermore, those skilled in the art will apprehend the advantageous simplicity of the elements described hereinabove for cementing a casing within a well hole. The use of complicated devices such as packers, wash pipes, etc., is obviated. It is to be noted that the cementing device has an interior diameter equivalent to the interior diameter of the casing itself, thereby not impairingthe effective area of the string. Moreover,'the

method of cementing is novel in' that the cement slurry is supported and suspended exteriorly of the casing upon a quiescent body of mud fluid.

Although specific embodiments of the invention have been described in detail, it will be apparent that numerous changes and modifications may be made without departing from the scone of this invention.

All such changes and modifications as come within the scope of the appended claims are embraced thereby.

I claim: v

1. In a method of cementing a combination string within a well hole, the steps of sealing apertures in a screen casing, lowering a string of imperforatecasing to which said sealed screen casing is attached into a well hole, circulating a fluid through said combination string, plugging the string above said sealed screen casing, opening passageways in the casing above the point at which it was plugged, admitting a cementitious material from said casing and passageways into the well hole, permitting said cementitious material to set, and then clearing the center of said casing and opening the apertures in I inserting a plug into the top of the casing,

introducing a cement slurry on top of said plug, introducing a top plug on top of said cement slurry, introducing and forcing a hydraulic fluid into the casing on top of said top plug to cause said bottom plug to open passageways in said combination string at a point above said screen, forcing the cement slurry through. said passa eways and upwardly around said imper orate casing, allowing said cement'slurry to set, and then clearing the center of said casing and opening the apertures in said screen.

3. In a method of cementing a combination string within a well hole, the steps of sealing apertures in a screen casing, lowering a string of imperforate casing to which said sealed screen casing is attached into a well hole, circulating a fluidthrough said combination string, plugging the string above said sealed screen casing, opening passageways in the casing above the point at which it was plugged, admitting a cementitious material from said casing and passageways into the well hole, and permitting said cementitious material to set.

4. In a method of cementing a combination string within a well hole, the steps of sealing apertures in a screen casing, lowering a string of imperforate casing to which said sealed screen casing is attached into a well hole, circulating a mud fluid through said combination string and upwardly around said screen casing, plugging the string above said sealed screen casing, opening passageways in the casing above said screen casing, forcing a cementitious material into said casing and through said passageways into the well hole and upwardly around said imperforate casing in said well hole, and permitting said cementitious material to set. 5. In a method of cementing a combination string within a well hole, the steps of sealing apertures in a screen casing, lowering a string of imperforate casing to which said sealed screen casing is attached into a well hole, circulating a mud fluid through said combination string and upwardly around said screen casing, plugging the string above said sealed screen casing, opening passageways in the casing above said screen casing, forcing a cementitious material into said casing and through said passageways into the well hole and upwardly around said imperforate casing in said well hole, permitting said cementitious material to set, and then clearing the center of said casing and opening the apertures in said screen.

6. A method of the character described comprising the steps of sealing apertures in a screen casing, lowering the screen casing into a well hole,v circulating fluid through said screen casing in said well hole, and opening the apertures in said screen casing while in said well hole.

7. In a. method of setting screen pipe and casing. in a well hole, the steps of lowering a screen pipe into a well hole, and circulating fluid downwardly through the center of said screen pipe and upwardly through the well hole around said screen pipe while restrictmg the flow of fluid through perforations in said screen.

8. In a method of setting screen pipe and casing in a well hole, the steps of sealing the apertures in a screen pipe, lowering the screen pipe into a well hole, circulating fluid downwardly through the center of said screen'pipe and upwardly through the well hole around said screen pipe to clear the well hole around said screen pipe, and then opening the apertures in said screen pipe while in said well hole.

9. In a method of setting screen pipe and casing in awell hole, the steps of app-lying a layer of cementitious material to the interior surfaces of a screen pipe, attaching said screen pipe to imperforate casing, lowering a string of imperforate casing to which said sealed screen pipe is attached into a well hole, circulating fluid downwardly through the center of said screen pipe and upwardly through the well hole around said screen pipe to clear the well hole surrounding said screen pipe, and then drilling out the internal layer of cementitious material on said screen pipe while preventing relative rotation of said screen pipe and casing.

10. A method of setting screen casing in a well hole, comprising the steps of sealing apertures in a screen casing with a fusible material,'lowering the sealed screen casing into a well hole, and then opening the apertures in said screen while in said well hole by the application of heat. I

11. In a method of setting screen casing in a well hole, the steps of sealing apertures in a screen casing with a cementitious composition adapted to disintegrate under the continued action of aqueous liquid, lowering the sealed screen casing into a well hole, and circulating fluid through said screen casing in said well hole. I

12. A screen casing provided with a plurality of apertures in the walls thereof, and a removable sealing means adjacent the interior surface of the screen casing, said sealing means being adapted to restrict flow of fluid through said apertures.

13. A screen casing provided with a plurality of apertures therein, and'a filler of sealing material in said apertures, said sealing material'being adapted to disintegrate Hndar continued contact with an aqueous 14. A screens casing comprising a casing provided with a plurality of apertures therein, and a lining of cementitious material on m the inner surfaces of said screen casing, said cementitious material being adapted to retard the flow of fluid through said apertures for apredetermined period of time and to weaken and partially disintegrate by continued contact with an aqueous fluid.

15. A screen casing provided with a plurality of apertures in the walls thereof, and

provided with a fusible sealing means adapted to retard flow of fluid through said apertures and to melt and open said apertures under action of heat.

16. A screen casing provided with a plurality of apertures in the walls thereof, said casing being provided with a lining of eementitious material on the inner surfaces, said cementitious material being adapted to retard flow of fluid through said apertures for a predeterminedperiod of time.

17. A screen casing provided with a plurality of apertures in the walls thereof, and a lining of cementitious composition containing hydraulic cement and a water soluble crystallizable salt, a major proportion of particles of hydraulic. cement in said composition being separated from each other by said salt in crystallized form, said cementitious composition retarding the fiow of fluid through said apertures.

18. A screen casing comprising a casing provided with a plurality of apertures therein, and a destructible, coherent lining of cementitious material on the inner surfaces of said screen casing, said lining being adapted to retard the passage of water through the apertures.

19. A screen casing provided with an inner destructible, coherent lining of cementitious material, and a fibrous material between said lining and said casing, said lining being adapted to retard the passage of water through said screen casing.

20. A string of casing comprising a tubular cementing device provided with internally threaded end portions, an imperforate casing threadedly connected to one end of said device and a screen casing, provided with a removable sealing means in its apertures. threadedly connected to the other end of said device, said cementing device including a tubular body portion, a plurality of outwardly flaring ports in the walls thereof, valve members in said ports and extending inwardly of said body portion, said valve members being adapted to be sheared off by application of force longitudinally of said 

